Native Image C API

Native Image provides a GraalVM-specific API to manage Java objects from the C/C++ languages, initialize isolates and attach threads. The C API is available when Native Image is built as a shared library and its declarations are included in the header file that is generated during the native image build.

/*
 * Structure representing an isolate. A pointer to such a structure can be
 * passed to an entry point as the execution context.
 */
struct __graal_isolate_t;
typedef struct __graal_isolate_t graal_isolate_t;

/*
 * Structure representing a thread that is attached to an isolate. A pointer to
 * such a structure can be passed to an entry point as the execution context,
 * requiring that the calling thread has been attached to that isolate.
 */
struct __graal_isolatethread_t;
typedef struct __graal_isolatethread_t graal_isolatethread_t;

/* Parameters for the creation of a new isolate. */
enum { __graal_create_isolate_params_version = 5 };
struct __graal_create_isolate_params_t {
    /* Version of this struct. Set to __graal_create_isolate_params_version after zeroing this struct. */
    int version;

    /* Fields introduced in version 1 */
    __graal_uword  reserved_address_space_size; /* Size of virtual address space to reserve for the heap. */

    /* Fields introduced in version 2. Internal usage, do not use. */
    const char    *auxiliary_image_path;                /* Path to an auxiliary image to load. */
    __graal_uword  auxiliary_image_reserved_space_size; /* Reserved bytes for loading an auxiliary image. */

    /* Fields introduced in version 3 */
    int            argc;                        /* Number of char* argument strings in argv. */
    char         **argv;                        /* Array of argument strings, parsed like command line arguments. */
    int            pkey;                        /* Isolate protection key or domain. Internal usage, do not use. */

    /* Fields introduced in version 4 */
    char           ignore_unrecognized_args;    /* Ignore unrecognized arguments in argv when 1. */
    char           _reserved_4;                 /* Internal usage, do not use. */

    /* Fields introduced in version 5 */
    char           _reserved_5;                 /* Internal usage, do not use. */
};
typedef struct __graal_create_isolate_params_t graal_create_isolate_params_t;

/*
 * Create a new isolate, considering the passed parameters (which may be NULL).
 * Returns 0 on success, or a non-zero value on failure.
 * On success, the current thread is attached to the created isolate, and the
 * address of the isolate and the isolate thread are written to the passed pointers
 * if they are not NULL.
 */
int graal_create_isolate(graal_create_isolate_params_t* params, graal_isolate_t** isolate, graal_isolatethread_t** thread);

/*
 * Attaches the current thread to the passed isolate.
 * On failure, returns a non-zero value. On success, writes the address of the
 * created isolate thread structure to the passed pointer and returns 0.
 * If the thread has already been attached, the call succeeds and also provides
 * the thread's isolate thread structure.
 */
int graal_attach_thread(graal_isolate_t* isolate, graal_isolatethread_t** thread);

/*
 * Given an isolate to which the current thread is attached, returns the address of
 * the thread's associated isolate thread structure.  If the current thread is not
 * attached to the passed isolate or if another error occurs, returns NULL.
 */
graal_isolatethread_t* graal_get_current_thread(graal_isolate_t* isolate);

/*
 * Given an isolate thread structure, determines to which isolate it belongs and returns
 * the address of its isolate structure. If an error occurs, returns NULL instead.
 */
graal_isolate_t* graal_get_isolate(graal_isolatethread_t* thread);

/*
 * Detaches the passed isolate thread from its isolate and discards any state or
 * context that is associated with it. At the time of the call, no code may still
 * be executing in the isolate thread's context.
 * Returns 0 on success, or a non-zero value on failure.
 */
int graal_detach_thread(graal_isolatethread_t* thread);

/*
 * Tears down the isolate of the passed (and still attached) isolate thread,
 * waiting for any attached threads to detach from it, then discards its objects,
 * threads, and any other state or context that is associated with it.
 * Returns 0 on success, or a non-zero value on failure.
 *
 * If this call blocks indefinitely, this means there are still Java threads running
 * which do not terminate after receiving the Thread.interrupt() event.
 * To prevent indefinite blocking, these threads should be cooperatively shut down
 * within Java before invoking this call.
 * To diagnose such issues, use the option '-R:TearDownWarningSeconds=<secs>' to detect
 * the threads that are still running.
 * This will print the stack traces of all threads that block tear-down.
 */
int graal_tear_down_isolate(graal_isolatethread_t* thread);

In addition to the C level API, you can use the JNI Invocation API to create an isolate from Java, expose and call Java methods embedded in a native shared library.

Native Image C API

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